This invention relates generally to the fastener art and more particularly to a snap-fit fastener assembly for attachment of a section of canvas or the like to an adjacent support structure.
Snap-fit fasteners are widely used and extremely important in the fastener art. Snap-fit fasteners provide a quick and efficient way to consistently and repeatably secure one body to another without additional tools.
A variety of snap-fit fasteners have been developed and are available for attaching one body to another and more specifically attaching a generally planar sheet member such as a section of canvas having a degree of stretch or elasticity to a generally rigid member or support structure. Many prior art fasteners incorporate two main components; a post attached to the rigid member, and a receptacle member securely attached to the generally planar sheet member or section of canvas.
The present invention was developed primarily for use with canvas covers or the like employed to cover boats or the like, and to overcome the shortcomings and disadvantages of prior art fastener systems as discussed hereinafter.
A first example of the prior art type of fastener system employs a split biasing ring retained inside of the receptacle portion attached to the cover. An inside diameter of the biasing ring is slightly smaller than an outside diameter of the post member. However, the post member is formed with a circumferential groove on the outside having a diameter generally less than or equal to the diameter of the biasing ring. The receptacle portion is engaged with the post portion by forcing the receptacle portion over the top of the post thereby expanding the biasing ring to enlarge the diameter thereof to force it over the top of the post. Once the receptacle is sufficiently forced over the post member the biasing ring engages the groove formed on the outside of the post member. A retaining fit is created when the biasing ring contracts into the annular groove formed on the post member. An example of this prior art design is illustrated in FIG. 9.
A second form of prior art fastening device employs a biasing member which is a formed spring pin. This second form of fastening device functions essentially in the same manner as the first form discussed hereinabove. The formed or split character of the spring clip permits the device to be designed for deeper spring clip/annular groove engagement. These first two types of fastener devices can be found in use on items ranging from clothing to boat covers.
A third form of fastening device functions to engage a sheet with a rigid member as described hereinabove but engages the receptacle member with a post member through an additional mechanical step. This type of fastening device is commonly called a "quarter-turn" locking device. The quarter turn device includes a post portion that has a locking member which is rotatable about an axis of the post. The post is axially inserted into an aperture formed in the receptacle portion and the locking portion is twisted one quarter turn to secure the receptacle portion onto the post. Typically, the locking portion and aperture are formed in cooperative irregular shapes such that a quarter turn of the locking portion prevents registration of the locking portion and the aperture thereby providing locking engagement.
A common problem with the prior art devices is that they typically are metallic and thus subject to corrosion, which is especially acute in salt water environments. Even if the metallic portions such as the biasing ring or spring clip are coated to prevent corrosion, repeated use of the clip either wears or flexes the coating off of the biasing portion thereby promoting corrosion. The problem with corrosion is that it stains or otherwise damages the canvas or sheet material used for the cover portion, and can become so sever as to prevent the fastener from functioning. Such characteristics are unacceptable for clothing or other visible applications. Also with these prior art designs is metal-to-metal contact between the post and the receptacle member which can and does result in galvanic action that accelerates corrosion. Here again the galvanic action which promotes corrosion is particularly strong in a salt water environment, where many canvas fastening systems are used.
A further problem with prior art devices is that a special tool must be employed to mount of assemble the receptacle portion with the cover or section of sheet material. Often a riveting operation is employed to crimp a lip portion of the receptacle portion through a hole formed in the cover material. The crimping operation requires time, training and specialized tools, and must be accurately performed in order to prevent cutting the material with an edge of the lip or damaging the fastener. This operation may damage the cover material and result in damaging the material thereby promoting pull out in which the receptacle disengages from the material portion when stresses are applied to the cover material.
Further, when a receptacle portion is damaged (for example through corrosion or impact) removal and replacement of the receptacle portion is very difficult and may in fact prevent reattachment of an identical receptacle portion. Since the receptacle portions are typically crimped onto the material as discussed above, removal may damage the cover material thereby enlarging the hole requiring a different receptacle portion to be used to replace the previous receptacle portion.
As an additional matter, once the receptacle portions are attached to the cover material and the posts are attached to the rigid material, such snaps are difficult to engage and disengage. Engagement difficulties arise because the cover material typically must be tensioned to engage the snap-fit fasteners. Tensioning of the material provides for a stronger cover which promotes protection of the covered area from environmental conditions as well as pre-stresses the covering material to prevent future sagging once the material naturally stretches. Since the receptacle portions of the snap lock fasteners have a generally low profile, they do not provide a convenient grip to engage or disengage the post members.